Through the adaptation of solution process such as printing method and ink-jet method to electronic devices, the application thereof to ultra-thin large displays, portable flexible displays, ID tags, or the like has been expected because of no need of using high vacuum process, high temperature process, or photolithographical process in manufacturing the devices; high adaptability to flexible substrates such as plastics; and high productivity.
For the development of electronic devices exerting the above performance, there have been required materials for constituting devices, which is formed by coating of a solution such as a printing process or the like, and has flexibility and high impact resistance.
Among display devices, organic EL devices have been the most promising devices in applying to plastic substrates, since they exhibit excellent image-quality performance and they are easy in terms of fabricating ultrathin devices.
Although there have been developed varieties of materials for emitting layer and for charge transport satisfying the above requirements at the present time, they are having a problem of being sensitive to surrounding environment of oxygen, water, and the like.
Consequently, there has been required to provide the organic EL device having a protective film thereon, in order to increase the environmental resistance. However, although a protective film is required to be manufactured also by means of the coating process when an organic EL device is formed on a flexible substrate by means of a coating process, a material in which the flexibility is expected is difficult to be obtained. Further, there arises a problem that the protective film manufactured by the manufacturing method using the solution process does not fully perform the functions.
As a typical example of the protective film for organic EL device, there is a method in which a thin film of silicon nitride or silicon dioxide is formed on an organic EL device by a CVD method and the like (refer to Patent Literature 1).
Furthermore, for increasing the adaptability to the device on a flexible substrate, there are proposed techniques of alternate lamination of inorganic materials and organic materials to relax the stress of the protective film in the device, or the like, as the protective film having increased resistance to flexural stress (refer to Patent Literature 2).
Moreover, as a technology of increasing specifically the resistance to moisture permeation among the functions of a protective film, there is a report or the like of dispersing phosphorus pentaoxide, silica gel, and the like as the water absorbent in the protective layer (refer to Patent Literature 3).
In all of the above-described exemplary developed techniques, the protective film of inorganic material which assures high barrier properties is formed by a vacuum process, and the film cannot satisfy the barrier properties required by organic EL devices.
Therefore, since all of the structural components of an organic EL device have been difficult to be manufactured by a solution process, the vacuum process has to be accommodated in the forming step, which raises a problem of being unable to exert the advantage of productivity inherent to the solution process.
Meanwhile, the fields of food-products, medical treatments, construction materials, and photography, the development of thick films having high gas-barrier and water vapor-barrier properties has been intensively progressing, and realization of high barrier properties has been attempted by adding a smectite silicate compound to a polymer material (refer to Patent Literature 4, and the like).
In this case, the addition of smectite silicate compound has been often performed to polymers, and the improvement in barrier properties by the addition of smectite silicate can be confirmed. However, the effect is far smaller compared with the level required by organic EL devices, by about five digits in terms of water vapor permeability, since the barrier properties of polymer are significantly poor, (refer to Patent Literature 5).
Furthermore, there is also another example in which mica is dispersed in a metal oxide glass by means of a sol-gel method. However, because of the characteristics of the manufacturing method, a dense film cannot be obtained, and thus high barrier properties cannot be attained (refer to Patent Literature 6, and the like).